Method of resealing pipe joints

ABSTRACT

A method for totally encapsulating and thereby sealing a leaking joint between pipes conducting fluid under pressures which may be as high as 30 p.s.i. or more involves filling a strong mould with a fluent encapsulant and exerting a balancing pressure in the encapsulant at least as high as that in the pipes either before encapsulant is injected into the mould or as a result of that injection. Apparatus for carrying this out includes a resilient mould, usually externally reinforced with a rigid shell, and means for either exerting a fluid pressure on encapsulant when in the mould or as it is injected into it so as to build-up the required balancing pressure. In one arrangement encapsulant is injected through one port against a gas counterpressure exerted through another port; in another arrangement encapsulant is injected through one port and controlled venting through and eventual closing off of another port during injection controls the pressure build-up. An encapsulant of low viscosity may initially be put into the mould by simple pouring, pressure in the mould being built-up later. Strain energy may be released from the mould to maintain pressure on an encapsulant which shrinks as it sets or cures. The mould is reusable.

Unite States Patent [191 Croft et al.

[ Dec. 16, 1975 METHOD OF RESEALING PIPE JOINTS [75] Inventors: Robert Croft, Bradford-on-Avon;

Raymond Lippiatt, Trowbridge, both of England [73] Assignee: Avon Rubber Company Limited,

Melksham, England [22] Filed: Mar. 19, 1973 [21] Appl. No.: 342,333

[30] Foreign Application Priority Data Mar. 20, 1972 United Kingdom 12982/72 [52] US. Cl. 264/36; 264/40; 264/262; 264/275 [51] Int. Cl. B29F 1/06 [58] Field of Search 264/36, 40, 262, 271, 275; 425/13, 14, 108, 129

[56] References Cited UNITED STATES PATENTS 333,011 12/1885 Hoeveler 264/262 3,265,782 8/1966 Rosengarten, Jr. et al 264/36 3,686,375 8/1972 Hall 264/262 Primary Examiner-Robert F. White Assistant ExaminerT. E. Balhoff ABSTRACT A method for totally encapsulating and thereby sealing a leaking joint between pipes conducting fluid under pressures which may be as high as 30 psi. or more involves filling a strong mould with a fluent encapsulant and exerting a balancing pressure in the encapsulant at least as high as that in the pipes either before encapsulant is injected into the mould or as a result of that injection. Apparatus for carrying this out includes a resilient mould, usually externally reinforced with a rigid shell, and means for either exerting a fluid pressure on encapsulant when in the mould or as it is injected into it so as to build-up the required balancing pressure. In one arrangement encapsulant is injected through one port against a gas counterpressure exerted through another port; in another arrangement encapsulant is injected through one port and controlled venting through and eventual closing off of another port during injection controls the pressure build-up. An encapsulant of low viscosity may initially be put into the mould by simple pouring, pressure in the mould being built-up later. Strain energy may be released from the mould to maintain pressure on an encapsulant which shrinks as it sets or cures. The mould is reusable.

8 Claims, 6 Drawing Figures U.S. Patent Dec. 16, 1975 Sheet10f4 3,927,158

U.S. Patent Dec.16,1975 Sheet2of4 3,927,158

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U.S. Patent Dec. 16, 1975 Sheet 4 of 4 METHOD OF RESEALING PIPE JOINTS FIELD OF THE INVENTION This invention relates to the formation of an encapsulation around a joint between hollow members intended to conduct a fluid under pressure (hereinafter referred to as pipes) for the purpose of ensuring fluid tight sealing of that joint. It proposes apparatus and a method which in various embodiments may be used either for the repair of a preexisting but worn or leaking joint or for the formation of a new joint.

BACKGROUND OF THE INVENTION There have been many proposals previously for packing and sealing around joints between hollow members which are under, or are intended to be under, pressure from inside. Most of these have been concerned with applying a sealing material just to the position where a leak path is, or is likely to occur.

The present invention is concerned with a different approach to this problem. It is concerned to encapsulate the whole of the joint area in an injectionmoulded block of material. This is necessary because in some types of joint, e.g. those where hook bolts are used, the interface where the leak path is, is not accessible for the application of a simple packing or seal strip.

This type of approach has hitherto been common when it has been desired to unify stripped cable ends where an electrical connection has been made. See, for example U.S. Pat. No. 2,463,231 and UK. Pat. No. 921,901. In the former, a readily expansible rubber tube is clamped around the joint and encapsulant is injected under pressure. The tube is then distorted by a U-clamp applied to one diameter, so as to apply pressure to the encapsulant. After hardening of the encapsulant, the tube is destructively removed. In the latter, a rigid mould has mechanical means for continually exerting pressure on an encapsulant within it, which may take the form of screws acting through the parts which served respectively for the injection of the liquid encapsulant and for the escape of air displaced by it.

But neither of these proposals faced the problem of encapsulating a joint between hollow members. The cables which were being treated were solid. There was no question, as there is here, that fluid could be escaping outwardly from the pipes. If this were permitted there would be a path of blow holes formed through the encapsulant while it was still liquid, weakening or even nullifying the sealing effect of the encapsulant.

In proposals for dealing specifically with leaking gas pipe joints, UK. Patent Specification No. 1,166,335 and U.S. Pat. No. 3,141,478 show rubber muffs (moulds) into which encapsulant was passed until the mould was full. In one of these Specifications (UK. Pat. No. 1,166,335) there is a realisation that a problem will arise when leakage is occurring from a joint, but it is only proposed to deal with this by injecting sealant at a faster rate than that of the leak. No attention is paid to this problem in U.S. Pat. No. 3,141,478.

The problem of leakage is not a serious one in the situations envisaged by these specifications since they are concerned only'with low-pressure joints. This is shown by the material of which their moulds are made.

The present invention is concerned with methods which can be carried out at pressures within the mould of up to 35 p.s.i. or even more, and apparatus that can be embodied to permit such methods to be performed. At these pressures, implying a pressure within the pipe of 30 p.s.i. or more, the methods of the previous proposals could not be used, or would (if used) only result in seals having leak paths through them due to the absence of balancing pressure outside the joint but within the mould.

SUMMARY OF THE INVENTION The invention therefore provides for exerting fluid pressure on the joint, at least as great as that within the pipes, before the completion of injection of encapsulant and maintaining either this pressure or higher at all times until the encapsulant is hardened. Thus any pressure within the pipes is at all times balanced or overbalanced during the hardening. It provides also a reusable mould for encapsulation, which has means for maintaining pressure on the encapsulant even if the latter shrinks during hardening.

In the broadest aspect of the invention there is provided a method of forming a pipe joint which consists in placing a temporary mould assembly about the joint which is to be encapsulated and injecting into the mould as suitable self-curing material,. hereafter referred to as the encapsulant, allowing it to harden and removing the mould. The mould assembly is one which has the capacity to exert a fluid pressure on the joint in reaction against the mould either before encapsulant is injected or by virtue of the encapsulant being injected to itself raise the pressure in the mould, and to maintain a pressure on the encapsulant within it as it hardens either by itself releasing its strain energy or by virtue of having means for exerting fluid pressure on the encapsulant as it cures. The first pressure is desirable to prevent fluid from the pipes leaking outward, the second because most encapsulants have a property of shrinking as they harden.

In one general form of the method, the mould assembly is placed around the whole of the joint to be encapsulated and is sealed to the pipe at each axial side, gas is passed under pressure into the mould so that there is sufficient pressure to stop leakage from the pipe into the mould, the encapsulant then being introduced under pressure. In another general form of the method encapsulant is introduced into the mould freely e.g. by pouring until the mould is at least partly full, and then pressure is applied by injecting encapsulant under pressure until the mould is full and at a pressure at least equal to that within the pipes.

The invention provides also apparatus for carrying out such methods which include a mould of resilient flexible material having at each axial side a shaped sealing strip for sealing to a pipe in a fluid tight manner, an inlet for encapsulating material between the sealing means, and means for regulating the fluid pressure acting between the sealing means and clamping means for clamping the mould around the pipe. Usually there will additionally be a rigid support shell outside the mould: usually also both the mould and the support shell are essentially semi-cylindrical. The mould may be provided with pressure regulating means for introducing gas under pressure and may have a relief system to control excess pressure. The inlet for encapsulant is preferably located on the lower half of the mould, when the mould is positioned for use.

DESCRIPTION OF PARTICULAR EMBODIMENTS Particular embodiments of the invention and of methods of carrying it out will now be described with reference to the accompanying drawings, wherein:

FIG. 1 is a view, looking along the pipe axis, of one face of a mould assembly placed in position over a pipe oint,

FIG. 2 is a section on the line XX of FIG. 1,

FIG. 3 shows diagrammatically a pressurizing and feed arrangement for the mould assembly,

FIG. 4 shows a modified part of the arrangement in FIG. 3,

FIG. 5 shows in radial section a typical encapsulation formed over a pre-existing joint, the example illustrated being of the hook bolt type, and

FIG. 6 shows a second embodiment, in transverse section through the joint.

An embodiment of mould assembly, and a particular method for carrying out encapsulation will be described with reference to FIGS. 1 to 5 and can be regarded as typical of its application to all types of pipe joints.

As this embodiment of the invention is intended primarily for the encapsulation of pre-existing joints it will be assumed throughout this part of the description that the joint is of the hook bolt type.

The joint shown has been formed between pipes 2 and 4 having pipe ends 1 and 3 respectively. End 3 is flared to receive the end 1 and has an external flange 5. It is pre-made so that hook bolts 6 are already in position engaging the flange 5 but it is desired to make the joint fluid tight where a leak has developed or a higher operating pressure is desired or it is desired to carry out preventative maintenance. This embodiment could also be used for the formation of an initial encapsulation around a newly made joint.

To form the encapsulation round the joint, a mould given the general reference 7 is placed over the joint.

This mould consists of polymeric or ply rubber/canvas material in the form of a sleeve 8 (made up of two generally semi-cylindrical parts) having at each end extruded seal sections 9 and 10 respectively having a series of circular ridges l1 moulded into the surface that are to engage the pipes. As seen in section (best seen in FIG. 2) the ridges are preferably saw-toothed with a substantially planar face facing towards the middle of the length of the mould, the better to retain pressure exerted from within the mould. The sleeve 8 is controlled on its radially outer surface by a cylindrical rigid shell 12 (made in two generally semi-cylindrical parts) which has a truly cylindrical portion and a frusto conical portion 13 also.

The shell is further reinforced by spines 14 which at one end projects at 15 at almost 90 to the spine portion 13. Each portion 15 has secured to it a narrow plate 16.

At the other end of the spine, plates 17 generally similar to plates 16 but shorter than those are secured perpendicular to the direction of the spine portion 14. Lying radially outside the seal parts 9 and 10 are straps l8 and 19 respectively which can be tightened by strap tensioners acting between upstanding lug ends of these straps 20.

The mould as a whole is made in two halves each generally semi-cylindrical so that it may be clamped about a pre-formed joint. The mould is in two semi-cylindrical portions as is the shell 12. The shell 12 is brought out to an upstanding lug 21 at each of its ends and these are secured together on each side of a rigid flange 22 of the mould 7. These end flanges are sandwiched be tween the lugs 21 and secured there by a nut and bolt on the line 23, and also between end lugs 24 of the straps 18 and 19 which are secured tightly together by nuts and bolts on the lines 25 FIG. 1. In this way a mould assembly may be tightly clamped in situ around a pre-formed joint and brought into fluid tight contact with a portion of pipe at each side of a joint.

Means are provided for bringing the interior of the mould, to a pressure greater than the working pressure in the pipe, preferably within 3 p.s.i. (pounds per square inch). This ensures that there is no outward leakage of fluid from the pipe into the mould at the beginning encapsulation. These means may also be used to bring the mould to a test pressure higher than the pressure which will be exerted on it during the encapsulation. They are indicated at FIG. 3, and consist of gas inlet 27 situated at top dead centre which leads via a sight tube 37, used in the injection operation, to a selfbleed regulator and a regulated supply source 38 of gas under pressure. In an alternative arrangement (FIG. 4) the self-bleed regulator is replaced by a manually operated value 39 to relieve excess pressure as indicated by a pressure gauge 41 situated in the line from a suppply source 40.

The inlet port 26 for the encapsulant is situated at the base of the mould 7 and is clipped to a flexible hose 30 which, through a valve 31, is connected to an injection system exemplified by feed cylinder 32 swept by a piston 33. Air under pressure, eg p.s.i. is led from a source 34 via a tap 35 and pressure regulator 36 to the upper end of the feed cylinder 32. Obviously many arrangements other than those shown here could be used.

To carry out a repair of a leaking joint using this embodiment of apparatus the leaking joint is first identified and exposed by excavation all around it. The area of the joint to be covered by the mould is cleaned, usually by shot-blasting, and when some encapsulants are to be used it will be primed.

In use, the mould assembly is assembled over and around the pipe joint.

The interior of the mould is brought up to a test pressure greater than the final encapsulation pressure to check it is not leaking, gas (e.g. nitrogen or natural gas) from source 38, 40 being used.

This pressure is then reduced to preferably within 3 p.s.i. of pipe pressure. This ensures that when encapsulant is present there will be no outward leakage of fluid from the pipe into the mould.

The pressure regulator 36 is set to the pressure desired for encapsulation and this pressure is used to drive encapsulant from cylinder 32 against the existing pressure in the mould 7 until it is completely filled, and can be seen by observation in the sight tube 37. When the encapsulant is visible in the sight tube it is temporarily clamped off, and the delivery pressure is maintained while any trapped gases rise into the signt tube from where they can be bled off. When by observation of the sight tube it is seen that all trapped gases are removed the outlet tube 27 is clamped off, and the sight tube may be removed. The flexible delivery hose is then clamped off allowing the injection equipment to be removed but still maintaining sufficient pressure on the encapsulant, which is maintained by the mould even when the encapsulant physically shrinks, when strain energy is released from the material of the mould (and,

to a very slight extent, from the support shell).

In an alternative stopping off procedure the flexible delivery hose is clamped off and the final encapsulation pressure applied by gas source 38, which remains open so as to exert a fluid pressure on the encapsulant, having ensured that there is sufficient encapsulant in the sight tube to ensure that any volumetric change due to expansion of the mould under this pressure leaves the mould completely full. In a variation on this method, gas source 38 is replaced by line gas taken from a tapping elsewhere on the surface of the pipe, and this line gas used to balance pressure on the mould. in cases of extreme leakage the leak itself could be used as the gas source and sight tube 37 stopped off, these methods achieving the same results as stated in the previous sentences. The encapsulant is left to cure under a pressure preferably 3% to greater than that in the pipes. The mould assembly, being made in segments, may then be removed non-destructively, giving a joint as shown in FIG. 5.

An arrangement of apparatus and method which is particularly useful when small leaks occur in a joint, or when a low-viscosity encapsulant is to be used, is shown in FIG. 6.

A mould 60 is as before, with spined reinforcing shell 61 outside it, but modified in that while a port 42 is at the top of the mould in use, an inlet port 43 for injected encapsulant is about 60 offset from it, at a level above the horizontal plane which passes through the central axis of the pipe 2. Both ports 42 and 43 are directly accessible, therefore, from the top of the mould assembly when in use. The port 43 has a valved input tube 44 releasably connected through a tube of any desired length to a riser pipe 45 set in a cover 46 of a pressure vessel 47. The cover 46 is releasable from the rest of the vessel 47 to allow access to an open-topped container 48 of liquid encapsulant. A permanently open end 49 of the riser dips into the encapsulant near the bottom of the container 48 when the cover 46 is sealed into the top of the vessel. A pressure pipe 49 in the cover is connectable to a source of gas under pressure.

To the port 42 there can be fitted a sight tube 50, preferably flexible so that it may itself form a valve by being pinched off. Alternatively a separate valve may be fitted above the sight tube. The top of the sight tube 50 has a vent pipe 51 to atmosphere.

To operate in the abovementioned conditions a simple funnel is attached to the port 42 in place of the sight tube. Liquid encapsulant is poured in until a major pair of the mould is full e.g. up to about the level indicated at 52, or more. Then the funnel is taken away the sight tube is fitted and encapsulant injected under pressure by application of fluid pressure inside the vessel 47 through the pipe 49, to force encapsulant up the riser 45 and through the port 43. By this means the mould is completely filled with encapsulant to a level observed in the sight tube and pressure due to the injection is exerted on that encapsulant. There is controlled venting of displaced gas through the valve in or above the sight tube 50.

Even if there was a leak at the bottom of the joint so that a train of bubbles was forming in the encapsulant before it was under pressure the exertion of pressure as a result of and by the action of injection at least balances the pressure within the pipes and further bubbling is stopped. In a low-viscosity encapsulant the bubbles of the train will have time to reach the sight glass and be vented before the encapsulant sets.

Then, the valve in or above the sight glass 50 and in the input tube 44 are closed off and the encapsulant left to'set under pressure.

There are many advantages to these processes and the principal ones will be pointed out. They do not require the dismantling of the pipe joint or the cutting off of mains pressure within the pipes being operated on. They are applicable with suitable moulds and support shells to pressures up to p.s.i. since over-balancing is provided to prevent blowing out of the fluid from the leaking joint into the encapsulant. The mould can adapt itself to mis-shaped surfaces and diameters of pipe which are not quite standard.

The mould, having an in-built degree of flexibility, will effectively allow sealing of a joint between two pipes whose axes are out of alignment.

As pressure is exerted on the mould from inside it expands slightly into the gaps provided in the shell. Thus the mould stores strain energy which can be released if the encapsulant shrinks during curing, which maintains an even pressure over the whole of the encapsulation. This even distribution of pressure is important as the transmitting qualities of the encapsulant will diminish as its sets. We have found for example when the mould is pressurised to 35 p.s.i. it is capable of retaining 25 p.s.i. if there is a 1.4% volume loss due to shrinkage of encapsulant.

The mould may be used advantageously as a split repair muff with or without the encapsulant. Depending on application the mould can be manufactured from:

a. Polymeric-materials b. Polymeric materials reinforced (for example with canvas) for use at higher pressures.

The mould and outer shells may be made in two equal halves as shown, or from a greater number of segments, particularly for the larger sizes of pipe. Depending on the construction of the mould, the pipe diameter and working pressure following combinations of mould and shell may be used, to give the desired characteristics for the release of strain energy:

i. A mould with a spined' reinforcing shell as described ii. A mould with a plain reinforcing shell iii. A mouldalone, without a shell.

The entire mould assembly is re-usable.

Lastly, of course, the outline of the mould or shell can be tailored to a particular type of pre-existing joint which it is expected to be used with to ensure the minimum possible volume of encapsulant per joint.

This system is suitable for most types of pipe joints, including underground pipe joints or those used for connection between vessels or any pressure fittings", which include:

Hook Bolt Stanton Wilson Screwed Gland Bolted Gland Lead Yarn Flange Joint Full and half-turned joint.

Encapsulants used can include the following:

Polyurethanes Liquid Rubber Polyester and Epoxy Resins with suitable flexlbilisers. These may be blended with concrete plastef 6r other suitable fillers to minimise cost.

lclaim:

1. In a method of encapsulating a joint between hollow members for conducting a fluid under pressure, wherein a mould is fitted externally around the joint to define a mould cavity of greater transverse section than any part of the joint and a fluent encapsulant is injected into the mould, the improvement consisting of sealing the mould in gas-tight fashion to the hollow members at each axial side of the joint, applying a pressure within the mould before the completion of injection of encapsulant which is at least as great as the pressure within the hollow members, at least maintaining such a pressure until hardening of the encapsulant, the pressure within the mould being controlledly applied and maintained by gas under pressure supplied from outside the mould before, during and after injection of encapsulant and until hardening of the encapsulant, and removing the mould to leave a sealed joint surrounded externally by hardened encapsulant.

2. In a method of encapsulating a joint between hollow members for conducting a fluid under pressure, wherein a mould is fitted externally around the joint to define a mould cavity of greater transverse section than any part of the joint and a fluent encapsulant is injected into the mould, the improvement consisting of sealing the mould in gas-tight fashion to the hollow members at each axial side of the joint, applying a pressure within the mould before the completion of injection of encapsulant which is at least as great as the pressure within the hollow members, at least maintaining such a pressure until hardening of the encapsulant, the pressure within the mould before and during injection of encapsulant being controlledly applied by gas under pressure acting to inject the encapsulant into the mouh, and pressure on the encapsulant after injection being maintained at least partly by the release of strain energy from the mould itself, and removing the mould to leave a sealed joint surrounded externally by hardened encapsulant.

3. A method of rescaling a leaking joint between pipes by encapsulation around it, and having a leak path from within the pipes to outside them, which includes securing a non-flexible multipart mould assembly about the joint to surround it and define an interrupted volume between the joint and a moulding element of the assembly, the mould assembly being secured in gas-tight fashion to the pipes at each axial side of the outer end of the leak path injecting into' the volume a curing encapsulant composition in fluent state,

raising the pressure in the volume to at least equal that within the pipes, that pressure being so raised before beginning injection of encapsulant, and pressure within the mould is controlledly applied and maintained at least equal to that within the pipes by gas under pressure supplied from outside the mould before, during and after inspection of encapsulant and until hardening of the encapsulant, allowing the encapsulant to harden, and removing the mould.

4. A method of rescaling a leaking joint between pipes by encapsulation around it, and having a leak path from within the pipes to outside them, which includes securing a non-flexible multipart mould assembly about the joint to surround it and define an interrupted volume between the joint and a moulding element of the assembly, the mould assembly being secured in gas-tight fashion to the pipes at each axial side to the outer end of the leak path injecting into the volume a curing encapsulant composition in fluent state, raising the pressure in the volume to at least equal that within the pipes, that pressure being so raised before beginning injection of encapsulant, and the pressure before and during injection of encapsulant is controlledly applied and maintained at least equal to that within the pipes by gas under pressure acting to inject the encapsulant into the mould, and pressure on the encapsulant after injection is maintained at least partly by the release of strain energy from the mould itself, allowing the encapsulant to harden, and removing the mould.

5. The improvement according to claim 1 wherein gas controlledly applied to and maintaining pressure on the encapsulant in the mould cavity from a source of gas under pressure through an outlet for encapsulant from the mould cavity.

6. The improvement according to claim 1 wherein gas pressure is controlledly applied to the encapsulant by controlledly releasing gas at above a predetermined pressure from out of an outlet for encapsulant from the mould cavity, as encapsulant is injected into the mould cavity.

7. Th. improvement according to claim 5 wherein the pressure applied and maintained is about 3 psi above the pressure of fluid in the hollow members.

8. The improvement according to claim 6 wherein the pressure applied and maintained is about 3 psi above tll: pressure of fluid in the hollow members.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTION PATENT NO. 3,927,158

DATED December 16, 1975 INVENTOR(S) Robert Croft and Raymond Lippiatt It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 4, after methods insert and moulds Column 4, line 59, delete "signt" and insert sight Column 8, line 7, delete "inspection" and insert injection Signed and Scaled ttu's Al test:

RUTH C. MASON C. MARSHALL DANN Arresting Officer (mnmz'ssioner ofParenrs and Trademarks 

1. IN A METHOD OF ENCAPSULATING A JOINT BETWEEN HOLLOW MEMBERS FOR CONDUCTING A FLUID UNDER PRESSURE, WHEREIN A MOULD IS FITTED EXTERNALLY AROUND THE JOINT TO DEFINE A MOULD CAVITY OF GREATER TRANSVERSE SECTION THAN ANY PART OF THE JOINT AND A FLUEENT ENCAPSULANT IS INJECTED INTO THE MOULD, THE IMPROVEMENT CONSISTING OF SEALING THE MOULD IN GAS-TIGHT FASHION TO THE HOLLOW MEMBERS AT EACH AXIAL SIDE OF THE JOINT, APPLYING A PRESSURE WITHIN THE MOULD BEFORE THE COMPLETION OF INJECTION OF ENCAPSULANT WHICH IS AT LEAST AS GREAT AS THE PRESSURE WITHIN THE HOLLOW MEMBERS, AT LEAST MAINTAINING SUCH A PRESSURE UNTIL HARDENING OF THE ENCAPSULANT, THE PRESSURE WITHIN THE MOULD BEING CONTROLLEDLY APPLIED AND MAINTAINED SUCH A PRESSURE UNTIL SURE SUPPLIED FROM OUTSIDE THE MOULD BEFORE, DURING AND AFTER INJECTION OF ENCAPSULANT AND UNTIL HARDENING OF THE ENCAPSULANT, AND REMOVING THE MOULD TO LEAVE A SEALED JOINT SURROUNDED EXTERNALLY BY HARDENED ENCAPSULANT.
 2. In a method of encapsulating a joint between hollow members for conducting a fluid under pressure, wherein a mould is fitted externally around the joint to define a mould cavity of greater transverse section than any part of the joint and a fluent encapsulant is injected into the mould, the improvement consisting of sealing the mould in gas-tight fashion to the hollow members at each axial side of the joint, applying a pressure within the mould before the completion of injection of encapsulant which is at least as great as the pressure within the hollow members, at least maintaining such a pressure until hardening of the encapsulant, the pressure within the mould before and during injection of encapsulant being controlledly applied by gas under pressure acting to inject the encapsulant into the mould, and pressure on the encapsulant after injection being maintained at least partly by the release of strain energy from the mould itself, and removing the mould to leave a sealed joint surrounded externally by hardened encapsulant.
 3. A method of resealing a leaking joint between pipes by encapsulation around it, and having a leak path from within the pipes to outside them, which includes securing a non-flexible multipart mould assembly about the joint to surround it and define an interrupted volume between the joint and a moulding element of the assembly, the mould assembly being secured in gas-tight fashion to the pipes at each axial side of the outer end of the leak path injecting into the volume a curing encapsulant composition in fluent state, raising the pressure in the volume to at least equal that within the pipes, that pressure being so raised before beginning injection of encapsulant, and pressure within the mould is controlledly applied and maintained at least equal to that within the pipes by gas under pressure supplied from outside the mould before, during and after inspection of encapsulant and until hardening of the encapsulant, allowing the encapsulant to harden, and removing the mould.
 4. A method of resealing a leaking joint between pipes by encapsulation around it, and having a leak path from within the pipes to outside them, which includes securing a non-flexible multipart mould assembly about the joint to surround it and define an interrupted volume between the joint and a moulding element of the assembly, the mould assembly being secured in gas-tight fashion to the pipes at each axial side to the outer end of the leak path injecting into the volume a curing encapsulant composition in fluent state, raising the pressure in the volume to at least equal that within the pipes, that pressure being so raised before beginning injection of encapsulant, and the pressure before and during injection of encapsulant is controlledly applied and maintained at least equal to that within the pipes by gas under pressure acting to inject the encapsulant into the mould, and pressure on the encapsulant after injection is maintained at least partly by the release of strain energy from the mould itself, allowing the encapsulant to harden, and removing the mould.
 5. The improvement according to claim 1 wherein gas controlledly applied to and maintaining pressure on the encapsulant in the mould cavity from a source of gas under pressure through an outlet for encapsulant from the mould cavity.
 6. The improvement according to claim 1 wherein gas pressure is controlledly applied to the encapsulant by controlledly releasing gas at above a predetermined pressure from out of an outlet for encapsulant from the mould cavity, as encapsulant is injected into the mould cavity.
 7. The improvement according to claim 5 wherein the pressure applied and maintained is about 3 psi above the pressure of fluid in the hollow members.
 8. The improvement according to claim 6 wherein the pressure applied and maintained is about 3 psi above the pressure of fluid in the hollow members. 